In the early years of molded flexible polyurethane foam development, a prepolymer or two-shot molding process was employed. This prepolymer process was objectionable for various reasons, including poor reproducibility or prepolymer quality, metering and mixing difficulties as a result of the viscous nature of the prepolymer and the water amine catalyst solution, instability in the pre-gel stage, and unduly long post-cure of the foam. With the introduction of organo-tin and amine catalysts and silicone surfactants, one-shot foam molding became possible. Hence, one-shot molded polyurethane foams conventionally may be prepared by admixing polyols and aromatic polyisocyanates, usually in the presence of a catalyst and a blowing agent. Curing of foams produced in such manner, however, requires that the mold employed be quickly heated to high temperatures, i.e., in excess of 300.degree.F. by any suitable means, such as gas ovens or microwave or infra-red heating, after charging the mold with the foamable reaction mixture and maintaining the mold content at said temperature for a period in excess of at least ten (10) minutes to ensure sufficient cure of the foam to permit removal thereof from the mold.
More recently, there has been developed a new type of molded polyurethane foam suitable for use in cushions, as insulation, as matresses and in other applications in which prior art polyurethane foams were used. The new type of foam can be processed at much lower temperatures through the use of new highly reactive high molecular weight polyols. In general, polyols used for conventional hot molding contained at most a 50/50 ratio of primary to secondary hydroxyl content, while highly reactive polyols used in cold molded high resiliency foams can have as high as an 85/15 ratio of primary to secondary hydroxyl groups. Terms such as cold molding, cold cure and high resilient foam have been used in connection with such foam products. Such foam products not only exhibit desirable properties, such as a latex-like feel, high sag factor and improved fire retardancy, but the production thereof requires lower processing temperatures and shorter cure cycles.
In conjunction with the preparation of this new class of cold molded polyurethane foams, a variety of stiffening or cross-linking curing agents have been used to increase the load bearing properties of the foam. Although both polyols and polyamines have been proposed for use in this application, only aromatic diamines have met with some success. Methylene-bis(o-chloroaniline), known in the art as MOCA, can be used; however, this material is a solid at room temperature and must be melted and kept molten while being utilized in the polyurethane foam manufacturing process. Similarly, other materials used in conjunction with the highly reactive polyols in the cold molding foam process are either highly viscous or solid at room temperature and must be heated prior to use. Other such materials are originally liquid at room temperature but separate at shipping temperatures commonly encountered in North America which can easily reach -10.degree.F., and can be as low as -30.degree.F. Products, such as methylenedianiline, are of particular interest for use as compounds which will react with the new reactive polyols since they are low in cost and readily available; however, they could be used only with difficulty because they are solid at room temperature and because of rapid reactivity which causes the formation of a gel prior to foaming.
Other materials which have been proposed as curing agents for polyurethane foams have a disadvantage in that they are incompatible with polyols commonly encountered in the manufacture of polyurethane foams.
It is therefore an object of this invention to provide an amine curing agent which is liquid at room temperature and is of relatively low viscosity.
Another object of the present invention is to provide a liquid amine curing agent which does not deposit solids on prolonged storage even at low temperatures.
Another object of this invention is to provide a curing agent which contains methylenedianiline.
Still another object of this invention is to provide a curing agent which is compatible with polyols used in manufacture of polyurethane foams.